Project Summary Semi-occluded vocal tract (SOVT) therapy is widely used to treat various voice disorders, including vocal fold lesions and primary muscle tension dysphonia. The mechanism of SOVT therapy has not been thoroughly studied. The added vocal tract, which is often a straw, changes both supraglottal acoustic impedance, and static supraglottal pressure; however, how these parameters independently contribute to the voice therapy have not been clarified. We would like to observe the supraglottal effects as well as the acoustic impedance effects of phonation independently and quantitatively. Our long-term aim is to improve upon current methods of SOVT therapy by exploring the underlying mechanisms and finding the optimal SOVT configurations that allow for the greatest increase in best quality of phonation. The proposed research consists of two independent phases. During Phase I, an excised canine larynx model will be used for the independent scientific evaluation and optimization of three variables in SOVT therapy ? (1) length of vocal tract extension, (2) vocal tract outlet constriction, and (3) regulated supraglottal pressure input. Extending the length and constricting the outlet of the vocal tract increases the acoustic impedance which then increases supraglottal pressure and the ease of phonation. The use of a regulated pressure input is a novel addition to SOVT therapy, which allows the supraglottal pressure to be directly controlled. Wide ranges of each SOVT variable will be examined individually to determine the optimal levels of each modification. Vocal phonation will be systematically monitored through dependent aerodynamic, electroglottographic, and acoustic parameters, including vocal efficiency. During Phase II, in human subjects, we will independently assess the three variables of SOVT therapy on subjects with and without hyperfunctional voice disorders. The results from the studies using an ex-vivo model gives information based solely on the mechanism, with an unscaled pattern; whereas, Phase II studies will give insight into the dynamic and behavioral reactions present in human subjects. Effects on vocal economy will be evaluated using aerodynamic, electroglottographic, and acoustic parameters as dependent variables. Through a standardized therapeutic task, the effect of the modifications of SOVT therapy can be isolated. The studies outlined in this proposal will evaluate optimal SOVT therapy configurations through independently testing the three SOVT modifications. Further, we also will include long and short duration therapeutic tasks. By testing each modification across different task durations, we can identify the minimal task duration to achieve significant benefits. Monitoring the immediate and long-term effects allows further insight on the overall impact that this voice therapy can have.